244 



ZOOLOGY 



SECT. 



six suckers with several hooks ; in the Temnocephalece (Fig. 190) 

 there is no anterior sucker, but the anterior end develops a row of 

 adhesive tentacles, while in Actinodactylella (Fig. 191) a series of 

 marginal tentacles are present in addition to both anterior and 

 posterior suckers. In general the monogenetic forms, being ex- 



l-'io. 100. Temnocephala. c. cirrus ; /. intestine ; j/i. mouth ; or. ovary ; ph. pharynx ; r. ,-. 

 receptaculuin vitelline ; t. testes ; t. s. terminal sac of excretory system ; v. vitellarium ; <-. a. 

 vesicula seminalis. (After Haswell.) 



ternal parasites, require more powerful organs of adhesion, and 

 have the suckers better developed than the digenetic, and often 

 armed with bristles or hooks. The suckers are used also in 

 locomotion, and here also there is necessity for greater develop- 

 ment in the case of the external parasites, which in many cases 

 move about with considerable activity after the looping fashion of 



